TLC2933A: PFD test

Hello Hoseok,

The PFD will only produce an output if FIN-A phase differs from FIN-B phase. So you need two input square waves, and their phases should be adjusted to see the output of the PFD. Since direct phase adjustment is not always provided as a function generator capability, the easiest way to generate phase skew is by mismatching the frequencies of the FIN-A and FIN-B pins. A clever choice of frequency mismatch, such as a 2:3 ratio, would fit well on an oscilloscope display and would generate segments with both VOH and VOL behaviors from the PFD.

Since the PFD is in HI-Z mode when the phases are well-aligned, it should be possible to see the HI-Z behavior by loading the PFD with a comparatively low impedance RC filter. VOH and VOL pulses will appear at the PFD output, travel through the RC filter, and should eventually be averaged at the capacitor to a voltage between 0V and 3V representing the average phase mismatch percentage. During HI-Z periods, the capacitor will drive the HI-Z output of the PFD through the resistor, which will settle at the capacitor voltage. The pulses would not be perfectly square as in Figure 2, but it should be a reasonable representation of the PFD behavior.

Regards,